In many ponds, lakes, and other bodies of water, the nutrient balance is such that phosphorus is the nutrient that limits the growth of algae. An increase in the amount of phosphorus in the water can cause an excess of algae. This can deplete the oxygen and the other nutrients in the water, to the detriment of fish and other life forms. It is therefore important to prevent excess phosphorus from entering the body of water.
Often, excess phosphorus comes from sewage. Sometimes, the excess phosphorus is in the effluent from small-scale domestic septic tank systems, and in some cases the factor that limits how many dwellings can be located in an area near a lake is the fact that any further dwellings will cause an unacceptable increase in the amount of phosphorus entering the lake.
The traditional way of limiting phosphorus has been to limit the number of dwellings. Conventional sewage treatment, especially of the kind carried out in a traditional domestic septic tank, has not been aimed at removing, and does not remove, the phosphorus to any substantive degree.
The invention is aimed at treating sewage water, to attenuate the phosphorus content thereof. Another aim is to provide a phosphorus treatment system which operates on the water as the water is passing through the septic-tank or other sewage treatment system, whereby the costs attributable solely to the phosphorus treatment system are minimised. Another aim is to provide a treatment system which requires nothing, or very little, by way of on-going attention and maintenance, over long periods of use.